In article <3860B28E.93334A63@pacbell.net>, lin### [at] povrayorg 
wrote:

> Ron Parker does it but I don't know how.

I have done hand coding of patches, but not with anything complex. 
Probably one of the two primitives I would use a modeller for(with the 
other being large meshes, although I can do small ones by hand). Hmm, 
actually, that isn't quite right, I do use the graphical spline editor 
in MacMegaPOV for lathe, sor, prism, etc objects. Does that count as a 
modeller?

All of the primitives can be hand coded, but the bicubic patch is 
usually done with a modeller. Of course, with the additions to the POV 
language of loops, conditionals, file I/O, and especially macros, you 
can generate the bicubic patches within the POV file.

One thing that may help: as I remember, the only easy way to get patches 
to tile is to overlap them. Imagine dividing them into 9 squares, the 
outermost ring of squares should overlap the surrounding patches, with 
the control points in the same position(did that make any sense?).

 ___________ _______
|   |   |   |   |   |
| - | - | * | + | + |
 ___________ _______
|   |   |   |   |   |
| - | - | * | + | + |
 ___________ _______
|   |   |   |   |   |
| - | - | * | + | + |
 ___________ _______

Squares with a - are in patch A, with a + are in patch B, with a * 
belong to both patches.
Also take a look at the scene description language reference in the 
documentation, it should be in section 4.5.2.1.

-- 
Chris Huff
e-mail: chr### [at] yahoocom
Web page: http://chrishuff.dhs.org/

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